Building New Grapevine Cordons: Only Strong Wood Allowed

Annie Klodd, UMN Extension Educator; John Thull, researcher, UMN Grape Breeding Program; and Matt Clark, Assistant Professor of Grape Breeding

Minnesota grape growers are familiar with the need to establish new cordons on spur-pruned vines. Not only do we do this when pruning newly-planted vines, but we also have to replace mature cordons when they are injured or killed by winter cold spells or disease. With proper planning and know-how, maintaining fruitfulness on each arm of every vine improves yields across the vineyard.

Photo: A grapevine with newly established cordons, near Mankato, MN.

In very general terms, the process of establishing a new cordon on spur-pruned vines is to find a strong cane from the previous growing season and tie it onto the trellis wire so that it will become the new cordon. We will call this cane the “renewal cane” for the remainder of the article. While this is the basic process, there is more to consider if it is to be done well. 

We typically do not want to just tie down the entire cane and move to the next vine. If done this way, the second half of the new cordon (further from the vine’s center) will often be too skinny and weak, or as viticulture expert Fritz Westover would say “wimpy.” 

The reasoning behind this: Every fruiting cane or sucker on a grapevine is thickest near the base or near the trunk, and becomes thinner toward the tip (the growing point). Because the cane grew throughout the season, the wood at the tip of the cane had less time to grow and is therefore not as thick nor hardy as the wood at the base. The buds are also smaller and less mature as a result. 

Therefore in many cases, if a full cane is set down in an attempt to establish an entire cordon at once, that new cordon will likely lack vigor and it may not be able to support a healthy crop or vigorous shoots in the coming years. In many cases, portions of the new cordon may not survive at all or will be largely unproductive. However, there are occasional exceptions to this. The amount of healthy wood and buds on a cane depends on the variety, soil nutrition and organic matter, and general health of the vine. Some varieties such as Itasca, if grown on soil with medium or high organic matter, can produce thick wood and healthy buds for several feet down the cane. We will get to this later.

Steps for establishing strong cordons:

When laying down a renewal cane, the goal is to retain the strong wood that is toward the base, and prune off the weaker wood toward the shoot tip. This often means establishing a new cordon in two segments, over two seasons. The amount pruned off should take into account the variety, wood diameter, and number of healthy buds present. 

First, remove any dead wood. Removal of the existing dead or damaged cordon should be completed during the winter while pruning. However, if a declining cordon is still producing some fruit, you may retain it and lay the renewal cane next to it for a more gradual replacement process. Having a fruitful cordon and a renewal cane laid side-by-side is a proactive solution to maintaining fruitfulness year after year (see photo below). 

The process described below applies to both approaches, however removing any dead and diseased wood is an important first step for any pruning practice.

Photo: A new cane in the process of being laid down next to the existing cordon, which is in declining health.

Second, choose a renewal cane to become the new cordon. The cane you use may come from the “head” or “crotch” of the vine (where the two cordons meet), lower on the trunk, or in some cases may just extend from an existing healthy, but too-short, cordon.

Examine it to make sure it is healthy and thick, without being a bull cane. See that the buds look plump and healthy, and that the wood is dark and flexible (not dry and brittle). Try to find canes that are at least the diameter of a pencil, but thinner than a sharpie, with buds spaced 3-4 inches apart.

Third, decide how much of the renewal cane to save, and where to make a pruning cut. A simple rule of thumb is to cut at the point along the cane where it becomes thinner than a pencil. Often, this will be about 15-18 inches down the cane, or after 4-7 buds, but can be further out if the cane was especially vigorous. 

Each bud along this cane (now cordon) will become a shoot with fruit in the coming summer. These shoots will then be trained or pruned to spurs for each additional year. This is why choosing the right cane, with healthy wood, large buds, and the proper diameter, is important.

When choosing where to cut, make the cut just past a healthy bud, ideally one that is oriented outward rather than vertically or downward. The shoot that eventually grows from that bud can be used to continue the length of your new cordon next year. 

Photo: The cane has been laid down for a new cordon, and trimmed about 15 inches down the wire, a couple centimeters past a healthy bud. The bud will produce a shoot that can be used to continue the length of the cordon next season.

What if the whole cane is thinner than a pencil? Try to find a better cane. If this is all you have to work with, then cut it back to the first 2-3 buds. It may not produce well next year, but if it is all you have to work with, it won’t hurt to try.

Variety and vigor differences when choosing renewal cane length

As mentioned previously, the amount of healthy wood and buds along a renewal cane, and therefore how much of the renewal cane to retain, depends somewhat on variety, age, and vigor of the vine. 

John Thull, researcher for the UMN grape breeding program, has years of experience working with UMN grape varieties and breeding selections at the UMN Horticulture Research Center. Through the years, John has observed differences due to variety, vine age, and vine health when establishing new cordons. 

According to John, the Frontenac family of varieties does best when the cordons are established over two seasons, using the process described above, leaving no more than 8-10 buds per renewal cane.

In contrast, mature Itasca vines, when grown on fertile soil with high organic matter, can sometimes produce 10-12 healthy, productive buds per cane before the cane diameter and bud hardiness diminishes. Many of the UMN varieties produce canes with 3” internodes (3” between buds). Leaving 12 Itasca buds spaced 3” apart on a renewal cane would give you a renewal cane that is 3 feet long, filling out the entire cordon length on vines spaced at 6 feet. In this case, you could potentially establish a full cordon in one season. In other cases, such as in the Itasca photos in the article, the vines are not vigorous enough to do that, and renewal canes must be cut shorter.

LaCrescent and Marquette can theoretically retain 10-12 healthy buds per renewal cane, as long as the cane remains thick and healthy, but ideal conditions and management are needed to make this happen. Therefore, assess cane and vine health and/or choose the more prudent route of making the pruning cut about 15 inches down the renewal cane.

Vines that are young, have smaller root systems, or are growing on lighter soil, are not capable of producing canes with higher levels of vigor, so the length of the renewal cane retained should be shorter than a more mature, vigorous vine. Additionally, many varieties are not as vigorous as Itasca.

Many labrusca-type vines, like Edelweiss, Brianna, and Concord, are genetically predisposed to producing longer internodes on average of 4" or more. This has implications on retraining choices, because you may leave a slightly longer renewal cane if the buds (nodes) are further apart but still healthy.

Fourth, tie down the renewal cane. Secure the remaining portion of the renewal cane loosely to the trellis wire with tapener tape or plastic fasteners (i.e. AgTies). Use enough ties so that the cordon is relatively parallel to the wire. Fasten them just loosely enough for the cordon to widen as it grows without being girdled by the wire or plastic ties.

Growers can also consider using two canes laid down in tandem, to ensure the success of at least one. But for this, John recommends cutting the two canes to two different lengths. As an example, one cane could be 4-7 buds long and the other could be 10-12 buds long, thus keeping production up during the cordon rejuvenation process.

Photo: A dead cordon and a 1-year-old sucker are seen side by side (left). The dead cordon and trunk are removed, and the sucker is taped down and trimmed to become the new cordon (right).

Impacts of weather and winter injury

This is Minnesota, so we cannot have a conversation about pruning without accounting for winter injury. Injury occurs on both buds and wood. Before renewing with canes, know how harsh the cold may have been to the buds and canes under consideration. Tender varieties commonly experience bud damage from ice crystal formation; anticipate that not all of the buds you retain on a renewal cane will be alive. Leaving a second cane is one way to compensate for this. Even hardier varieties won't always behave exactly 'textbook' due to other past season circumstances, like low GDD, high yields, excessive rain, canopy density, or grower management mistakes.

Applying This to Pruning New Vines

This same principle applies to pruning one-year old vines. Prune one-year old vines back to the point where the canes are healthy and the diameter of a pencil, with plump buds. Some growers recommend pruning every new vine back to just 2 buds. However, it is not necessary to prune back to just 2 buds unless the cane really lacks girth and vigor. Some varieties establish much faster than others, and growth is affected by soil and management in the first year, so always pruning back to 2 buds is too broad of a generalization. If you are able to keep more buds and cane length, they will give you more options for establishing health trunks next year.

When multiple canes/suckers are present, choose the strongest canes and remove the excess canes. In addition, cut off thin lateral shoots that have formed. In cases where winter injury is suspected, it is ok to leave extra canes as “insurance” in case one or more die over the winter.

Below is a before-and-after comparison of a one-year old Itasca vine being pruned back in preparation for Year 2:

Photos: A vigorous one-year-old Itasca vine before pruning and training (left) and after pruning and training new cordons to each side (right). 

Cane Pruning

While cane pruning is not widely adopted in Minnesota, growers do inquire about this practice as an alternative to spur pruning (pruning to spurs along a semi-permanent cordon). In cane pruning, the cordon is renewed every year by a 1-year-old cane. 

The question then, related to this topic, is how long to cut back the canes when cane pruning. This varies depending on the variety. Cane pruning is best suited for varieties that fruit well between the 5th and 10th buds on a cane. When laying down a cane, the cut should still be made before the point where the wood becomes very skinny and weak, but try to retain 10 buds if possible. Do not make the cane so long that it overlaps with the neighboring vine. Basic information on cane pruning can be found here.